This could be a problem with the TLS 1.3 Early Data feature also known as Zero Round Trip Time Resumption (0rtt). You can try to set security.tls.enable_0rtt_data = false on the about:config page to disable this feature until this is fixed by Google or Mozilla to see if that helps.

See also:

• /questions/1376015 Issue with most Google sites on Firefox v100 64bit

Tried that, still not loading. It loads part of the time, but not always. And, had not tried the "about:config" for that problem so was something else to try to fix Firefox problems!

Start Firefox in Troubleshoot Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration or if userChrome.css/userContent.css is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Troubleshoot Mode start window

• https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Sigh, tried that, still loads only part of the time.. Mozilla, get your act together or going to have to switch to a different default browser!

You can also contact Google about this as well since this is a Google product not a Firefox online service.